A developing cartridge that can be mounted in a drum cartridge is well known in the art. One such drum cartridge includes a photosensitive drum.
The developing cartridge has a rib positioned at a side surface of the developing cartridge. When the developing cartridge is mounted to the drum cartridge, the rib is pressed by a pivot arm provided at the drum cartridge. Through this operation, a developing roller provided at the developing cartridge is pressed toward the photosensitive drum of the drum cartridge.